Overview

The serial port routines normally use the USART_UDRE_vect, USART_RX_vect, USART0_UDRE_vect, USART0_RX_vect, USART1_UDRE_vect, and USART1_RX_vect interrupts, so they will conflict with any code that also uses these interrupts.

On the 3pi robot, Orangutan SV, Orangutan LV-168, and Baby Orangutan B, using these functions will cause the red user LED functions to stop working, because the red LED is on the same pin as the UART transmitter (PD1/TXD). When the AVR is not transmitting bytes on TXD, the red LED will be on. When the AVR is transmitting bytes on TXD, the red LED will flicker.

On the Orangutan SVP, using these functions to control UART0 will cause the red user LED functions to stop working, because the red LED is on the same pin as the UART0 transmitter (PD1/TXD0). When the AVR is not transmitting bytes on TXD0, the red LED will be off. When the AVR is transmitting bytes on TXD0, the red LED will flicker. However, the AVR on the Orangutan SVP has two UARTs, so if you want to use the red LED and you only need one UART then you can use UART1 instead of UART0.

Usage Examples

Example code for making the 3pi Robot into a serial slave, controlled by another microcontroller, is given in Section 10.a of the Pololu 3pi Robot User’s Guide. This library also comes with an example program in libpololu-avr\examples:

serial1

#include <pololu/orangutan.h>
/*
* serial1: for the Orangutan controllers and 3pi robot.
*
* This example listens for bytes on PD0/RXD. Whenever it receives a byte, it
* performs a custom action. Whenever the user presses the middle button, it
* transmits a greeting on PD1/TXD.
*
* The Baby Orangutan does not have a green LED, LCD, or pushbuttons so
* that part of the code will not work.
*
* To make this example compile for the Orangutan SVP, you
* must add a first argument of UART0 to all the serial_*
* function calls.
*
* http://www.pololu.com/docs/0J20
* http://www.pololu.com
* http://forum.pololu.com
*/
// receive_buffer: A ring buffer that we will use to receive bytes on PD0/RXD.
// The OrangutanSerial library will put received bytes in to
// the buffer starting at the beginning (receiveBuffer[0]).
// After the buffer has been filled, the library will automatically
// start over at the beginning.
char receive_buffer[32];
// receive_buffer_position: This variable will keep track of which bytes in the receive buffer
// we have already processed. It is the offset (0-31) of the next byte
// in the buffer to process.
unsigned char receive_buffer_position = 0;
// send_buffer: A buffer for sending bytes on PD1/TXD.
char send_buffer[32];
// wait_for_sending_to_finish: Waits for the bytes in the send buffer to
// finish transmitting on PD1/TXD. We must call this before modifying
// send_buffer or trying to send more bytes, because otherwise we could
// corrupt an existing transmission.
void wait_for_sending_to_finish()
{
while(!serial_send_buffer_empty());
}
// process_received_byte: Responds to a byte that has been received on
// PD0/RXD. If you are writing your own serial program, you can
// replace all the code in this function with your own custom behaviors.
void process_received_byte(char byte)
{
switch(byte)
{
// If the character 'G' is received, turn on the green LED.
case 'G':
green_led(1);
break;
// If the character 'g' is received, turn off the green LED.
case 'g':
green_led(0);
break;
// If the character 'c' is received, play the note c.
case 'c':
play_from_program_space(PSTR("c16"));
break;
// If the character 'd' is received, play the note d.
case 'd':
play_from_program_space(PSTR("d16"));
break;
// If any other character is received, change its capitalization and
// send it back.
default:
wait_for_sending_to_finish();
send_buffer[0] = byte ^ 0x20;
serial_send(send_buffer, 1);
break;
}
}
void check_for_new_bytes_received()
{
while(serial_get_received_bytes() != receive_buffer_position)
{
// Process the new byte that has just been received.
process_received_byte(receive_buffer[receive_buffer_position]);
// Increment receive_buffer_position, but wrap around when it gets to
// the end of the buffer.
if (receive_buffer_position == sizeof(receive_buffer)-1)
{
receive_buffer_position = 0;
}
else
{
receive_buffer_position++;
}
}
}
int main()
{
// Set the baud rate to 9600 bits per second. Each byte takes ten bit
// times, so you can get at most 960 bytes per second at this speed.
serial_set_baud_rate(9600);
// Start receiving bytes in the ring buffer.
serial_receive_ring(receive_buffer, sizeof(receive_buffer));
while(1)
{
// Deal with any new bytes received.
check_for_new_bytes_received();
// If the user presses the middle button, send "Hi there!"
// and wait until the user releases the button.
if (button_is_pressed(MIDDLE_BUTTON))
{
wait_for_sending_to_finish();
memcpy_P(send_buffer, PSTR("Hi there!\r\n"), 11);
serial_send(send_buffer, 11);
// Wait for the user to release the button. While the processor is
// waiting, the OrangutanSerial library will take care of receiving
// bytes using the serial reception interrupt. But if enough bytes
// arrive during this period to fill up the receive_buffer, then the
// older bytes will be lost and we won't know exactly how many bytes
// have been received.
wait_for_button_release(MIDDLE_BUTTON);
}
}
}